Semiconductor device having gate electrode and impurity diffusion layer different in conductivity type and method of manufacturing the same

ABSTRACT

A poly-crystal silicon layer is formed on an N-type silicon substrate via an oxide film. A contact hole is formed on the poly-crystal silicon layer by applying a photoresist mask and further by patterning a predetermined contact portion between a polyside gate and a diffusion layer. Thereafter, a P +  diffusion layer is formed by ion implantation with the use of the same photoresist mask. Further, a tungsten siliside layer is deposited all over the substrate. Or else, after the contact hole has been formed, the tungsten siliside layer is deposited, and then the P +  diffusion layer is formed by ion implantation. Alternatively, after the contact hole has been formed, a first ion implantation is made; and after the tungsten siliside layer has been deposited, a second ion implantation is made to form the P +  diffusion layer. In the manufacturing method as described above, an ohmic contact can be realized between the polyside gate electrode and the diffusion layer via the tungsten siliside layer, irrespective of the conductivity types of the gate electrode and the diffusion layer, without use of any additional metallic layer other than the polyside.

This is a continuation of application Ser. No. 08/141,197, filed on Oct. 21, 1993, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device having a gate electrode and an impurity diffusion layer different in conductivity type from each other, and a method of manufacturing the same semiconductor device, and in particular to semiconductor devices suitably used for a CMOS cell array in a memory LSI.

2. Description of the Prior Art

In an LSI (large scale integrated circuit), it is preferable that the resistances of electrodes and wiring are as low as possible, so that metallic material is suitable as the electrode and wiring material from the practical standpoint. In the case of a MOS transistor, in particular where a metallic layer is formed on an oxide film, however, since the atoms of the metal enter the oxide film or react with the oxide film, there exists a problem in that the breakdown voltage decreases or the interface level increases. Accordingly, poly-crystal silicon has been so far used, because the resistance thereof is not so high and can be further reduced by addition of impurities thereto.

In the case of the poly-crystal silicon, however, even if any impurities are added thereto, there exists a limit of the resistance to be lowered. Accordingly, with the advance of the further microminiaturization and the higher operation speed of the MOS transistor, the above-mentioned resistances of the electrodes and the wiring have raised a new problem more and more in the field of the LSI. Therefore, finally a realization of an electrode wiring material lower in resistance than the poly-crystal silicon has been required.

For satisfying this need, recently, there has been developed a high men, ting point metal, which can be easily replaced with the poly-crystal silicon because the specific resistance thereof is lower by one figure (cipher) than that of the poly-crystal silicon and further the characteristics thereof are similar to those of the poly-crystal silicon. The above-mentioned high melting point metal is used as the electrode and wiring material for the CMOS transistor, in the form of a two-layer lamination structure of this metal layer (or a siliside layer containing this metal) and a poly-crystal silicon layer. In particular, a combination of the high melting point metal siliside and the poly-crystal silicon layer has been well known under the name of "polyside".

When the high melting point metal or the siliside layer is formed on an oxide film via the poly-crystal silicon layer, it is possible to reduce the resistance of the material containing metal and further to eliminate the above-mentioned problems with respect to the metal atoms.

On the other hand, in the LSI, in particular in the case of the memory cell which is microminiaturized more and more, it is effective that the gate electrodes are used as the wiring layer as they are and additionally can be connected directly to the diffusion layer in order to improve the integration rate (density).

The conventional process of manufacturing an ohmic contact portion between the polyside gate and the diffusion layer in the SRAM (static random access memory) LSI memory cell array will be described hereinbelow with reference to FIGS. 1A to 1D.

First, as shown in FIG. 1A, a field oxide film 302 is formed on a P-type semiconductor substrate 301 in accordance with a selective oxidization method. Further, a gate oxide film 303 with a film thickness of about 150 Å is formed, and further a poly-crystal silicon layer 304 with a film thickness of about 500 to 1000 Å is deposited on the gate oxide film 303 as the gate electrode wiring material.

Secondly, as shown in FIG. 1B, a contact hole 305 is formed by removing the gate oxide film 303 and the poly-crystal silicon layer 304, on which an ohmic contact portion between the gate electrode and the diffusion layer is to be formed, in accordance with lithographic technique and etching technique. Successively, a poly-crystal silicon layer 306 with a film thickness of about 500 to 1000 Å is deposited all over the surface of the substrate 301 in the same way as with the case of the polyp-crystal silicon layer 304.

Thereafter, as shown in FIG. 1C, an N-type impurity is added to the poly-crystal silicon layer 304 and the poly-crystal silicon layer 306 in accordance with P diffusion technique or ion implantation technique and annealing, and simultaneously an N-type diffusion layer 307 is formed on the surface region corresponding to the contact hole 305 of the substrate 301.

Further, as shown in FIG. 1D, a high melting point metal siliside layer 308 with a film thickness of about 1000 Å is formed on the poly-crystal silicon layer 306 by sputtering tungsten siliside. The presence of this siliside layer 308 serves to reduce the resistance of the gate wiring.

In the above-mentioned conventional process of manufacturing the semiconductor device as described above, when the ohmic contact is formed between the wiring formed by a lamination layer (composed of the impurity-added poly-crystal silicon layer 306 and the siliside layer 308) or the gate electrode of the MOSFET and the diffusion layer 307 formed on the silicon substrate 301, the conductivity type of the polyside layer 308 and the diffusion layer 307 must be the same as each other (N-type in the case of FIGS. 1C and D).

That is, in the case of the gate electrode to which an N-type impurity is added, the diffusion layer contacting the gate electrode to which the N-type impurity is added must be the same N conductivity type. In the same way, in the case of the gate electrode to which a P-type impurity is added, the diffusion layer contacting the gate electrode to which the P-type impurity is added must be the same P conductivity type.

Therefore, in a CMOS circuit of the SRAM memory cell, when the gate electrode is required to be connected to the impurity diffusion layer of different conductivity type, it has been so far necessary to use another metallic wire (e.g., Al) other than the polyside or to form the N-type region and the P-type region separately from each other by implanting ions into the polyside wiring. In the case where Al wiring is used, however, there exist problems in that the device element cannot be microminiaturized and further the number of manufacturing steps increases, thus resulting in a higher cost. In the case where two regions of different conductivity types are formed by ion implantation, however, there exists another problem in that since the conductivity type of the gate electrode is closely related to the threshold voltage of the MOSFET, the conductivity type cannot be easily determined under consideration of only the gate electrode and the diffusion layer, in addition to the problems with an increase of the number of manufacturing steps due to ion implantation and with a higher cost.

SUMMARY OF THE INVENTION

With these problems involved in the conventional semiconductor device in mind, the object of the present invention is to provide a semiconductor device and the method of manufacturing the same semiconductor device, by which an ohmic contact between the gate electrode and the impurity diffusion layer can be realized, irrespective of the conductivity types of the gate electrode and the diffusion layer, without use of any additional metallic wiring other than the polyside.

To achieve the above-mentioned object, the present invention provides a semiconductor device comprising: a silicon substrate of a first conductivity type; an impurity diffusion layer of a second conductivity type opposite to the first conductivity type, formed on a surface of said silicon substrate; a poly-crystal silicon layer of the first conductivity type, formed on said silicon substrate via an oxide film; a contact hole formed on a part of the oxide film and said poly-crystal silicon layer, passing through from surfaces of said poly-crystal silicon layer and the oxide film to a surface of said impurity diffusion layer; and an electrode wiring material layer containing metal, formed on said silicon substrate, for connecting said poly-crystal silicon layer and said silicon substrate through said contact hole.

Further, a first aspect of the present invention provides a method of manufacturing a semiconductor device, comprising the steps of: forming a poly-crystal silicon layer of a first conductivity type on a silicon substrate of the same first conductivity type via on an oxide film; forming a contact hole passing through from surfaces of the poly-crystal silicon layer and the oxide film to a surface of the silicon substrate, by removing a part of the poly-crystal silicon layer of the first conductivity type and the oxide film; forming an impurity diffusion layer of a second conductivity type opposite to the first conductivity type, by ion-implanting and diffusing an impurity of the second conductivity type to a surface region exposed through the formed contact hole on the silicon substrate and by further activating the ion-implanted and diffused layer; and forming an electrode wiring material layer containing metal, to connect the formed poly-crystal silicon layer and the formed impurity diffusion layer on the silicon substrate.

In the above-mentioned method, the diffusion layer is first formed by adding an impurity of the second conductivity type to the substrate in accordance with the ion implantation through the formed contact hole. Thereafter, the electrode wiring material layer is formed to connect the diffusion layer and the poly-crystal silicon layer.

Further, a second aspect of the present invention provides a method of manufacturing a semiconductor device, comprising the steps of: forming a poly-crystal silicon layer of a first conductivity type on a silicon substrate of the same first conductivity type via on an oxide film; forming a contact hole passing through from surfaces of the poly-crystal silicon layer and the oxide film to a surface of the silicon substrate, by removing a part of the poly-crystal silicon layer of the first conductivity type and the oxide film; forming an electrode wiring material layer containing metal, to connect the formed poly-crystal silicon layer and a portion exposed through the formed contact hole on the silicon substrate; and forming an impurity diffusion layer of a second conductivity type opposite to the first conductivity type, by adding an impurity of the second conductivity type to the formed electrode wiring material layer, by diffusing the added impurity of the second conductivity type to the exposed surface region on the silicon substrate, and by further activating the impurity-added and diffused layer.

In the above-mentioned method, the contact hole is first formed. Thereafter, the impurity added to the electrode wiring material layer is diffused into the substrate to connect the diffusion layer and the poly-crystal silicon layer.

Further, a third aspect of the present invention provides a method of manufacturing a semiconductor device, comprising the steps of: forming a poly-crystal silicon layer of a first conductivity type on a silicon substrate of the same first conductivity type via on an oxide film; forming a contact hole passing through from surfaces of the poly-crystal silicon layer and the oxide film to a surface of the silicon substrate, by removing a part of the poly-crystal silicon layer of the first conductivity type and the oxide film; forming an ion implantation region by ion-implanting an impurity of a second conductivity type opposite to the first conductivity type to a surface region exposed through the formed contact hole on the silicon substrate; forming an electrode wiring material layer containing metal on the silicon substrate, to connect the ion-implantation region of the impurity of the second conductivity type and the formed poly-crystal silicon layer; and forming an impurity diffusion layer of the second conductivity type, by adding an impurity of the second conductivity type to the formed electrode wiring material layer, by diffusing the added impurity of the second conductivity type to the exposed surface region on the silicon substrate, and by further activating the impurity-added and diffused layer together with the ion-implanted impurity.

In the above-mentioned method, the connection structure between the diffusion layer and the poly-crystal silicon layer can be attained in combination of the above-mentioned first and second methods.

Further, in the above-mentioned semiconductor device and the manufacturing methods, a simple high melting point metal can be used as the electrode wiring material containing metal. Alternatively, a siliside containing a high melting point metal can be used as the electrode wiring material containing metal. Further, the practical examples of the high melting point metal are tungsten, molybdenum, titanium, cobalt, tantalum, etc.

In the semiconductor device and the method of manufacturing the same semiconductor device according to the present invention, since the electric contact between the gate electrode and the impurity diffusion layer can be realized by use of the metal-containing material of polyside structure, it is possible to connect the gate electrode and the impurity diffusion layer whose conductivity types are different from each other, without use of any additional metallic wiring other than the polyside.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D are cross-sectional views for assistance in explaining a conventional method of manufacturing the semiconductor device;

FIGS. 2A to 2E are cross-sectional views for assistance in explaining a first embodiment of the method of manufacturing the semiconductor device according to the present invention; and

FIGS. 3A to 3F are cross-sectional views for assistance in explaining a second embodiment of the method of manufacturing the semiconductor device according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the method of manufacturing the semiconductor device according to the present invention will be described hereinbelow with reference to FIGS. 2A to 2E.

First, as shown in FIG. 2A, a field oxide film 102 is formed on an N-type semiconductor substrate 101 in accordance with a selective oxidization method. Further, a gate oxide film 103 with a film thickness of about 150 Å is formed within an HC-100% oxidizing atmosphere at 800° C., for instance, and further a poly-crystal silicon layer 104 with a film thickness of about 1000 Å is deposited on the gate oxide film 103 in accordance with chemical vapor deposition technique, for instance.

Secondly, as shown in FIG. 2B, an N⁺ impurity is added into the poly-silicon layer 104 in accordance with a P diffusion technique (e.g., P diffusion technique at 850° C. for 30 min) or an As ion implantation technique (e.g., acceleration energy: 30 keV, dose: 5×10¹⁵ cm⁻²).

Thereafter, as shown in FIG. 2C, a photoresist mask 105 is applied onto the poly-silicon layer 104 by a predetermined film thickness (e.g., 1.5 μm). Further, a predetermined ohmic contact portion (at which a gate and a diffusion layer are to be brought into contact with each other) is patterned by the lithographic technique, and further the gate oxide film 103 and the poly-crystal silicon layer 104 are both removed at only the predetermined ohmic contact portion between the gate electrode and the diffusion layer in accordance with the anisotropic etching technique and ammonium fluoride etching technique, in order to form a contact hole 106. Further, a P⁺ diffusion layer 107 is formed by use of the same photoresist mask 105 in accordance with the ion implantation technique. In this ion implantation technique, BF₂ ions are implanted at the acceleration energy of 35 keV and the dose of 3×10¹⁵ cm⁻². To protect the Si substrate from the ion implantation, it is also possible to effect the ammonium fluoride (NH₄ F) etching, after the poly-crystal silicon has been etched by RIE (reactive ion etching) and further the ions have been implanted under the condition that the oxide film is kept remaining.

Further, as shown in FIG. 2D, a tungsten siliside layer 108 with a film thickness of about 1000 Å is deposited all over the surface thereof by the sputtering technique.

Further, as shown in FIG. 2E, the poly-crystal silicon layer 104 and the tungsten siliside layer 104 are both patterned simultaneously by use of the lithographic technique and the anisotropic etching technique in combination. And then, BF₂ ions are again implanted at the acceleration energy of 35 keV add the dose of 3×10¹⁵ cm⁻² to form a P⁺ diffusion layer 107a by using the gate electrode (the gate oxide film 103 and the poly-crystal silicon layer 104) as a mask.

As described above, in the above-mentioned first embodiment, since the ohmic contact between the gate wiring (the poly-crystal silicon layer 104) and the impurity diffusion layer 107a can be attained by intervening the metal (the tungsten siliside layer 108) of polyside structure, it is possible to enable an ohmic contact between the gate electrode 103, 104 and the impurity diffusion layer 107a whose conductivity type are different from each other, without use of any metallic wiring other than the polyside. Accordingly, even when a two-layer gate electrode including a poly-crystal silicon layer of a first conductivity type is required to be connected to an impurity diffusion layer of a second conductivity type opposite to the first conductivity type, as with the case of the CMOS circuit of the SRAM memory cell, no metallic wiring other than the two-layer wiring is required, thus contributing to a further micro-miniaturization of the device, markedly.

A second embodiment of the method of manufacturing the semiconductor device according to the present invention will be described hereinbelow with reference to FIGS. 3A to 3F, in which the manufacturing steps shown in FIGS. 3A and 3B are substantially the same as those shown in FIGS. 2A and 2B, respectively.

First, as shown in FIG. 3A, a field oxide film 202 is formed on an N-type semiconductor substrate 201 in accordance with the selective oxidization method. Further, a gate oxide film 203 with a film thickness of about 150 Å is formed within an HC-100% oxidizing atmosphere at 800° C., for instance, and further a poly-crystal silicon layer 204 with a film thickness of about 1000 Å is deposited on the gate oxide film 203 in accordance with the chemical vapor deposition technique, for instance.

Secondly, as shown in FIG. 3B, an N⁺ impurity is added into the poly-silicon layer 204 in accordance with the P diffusion technique (e.g., P diffusion technique at 850° C. for 30 min) or As ion implantation method (e.g., acceleration energy: 30 keV, dose: 5×10¹⁵ cm⁻²).

Thereafter, as shown in FIG. 3C, a photoresist mask 205 is applied onto the poly-silicon layer 204 by a predetermined film thickness. Further, a predetermined ohmic contact portion (at which a gate and a diffusion layer are to be brought into contact with each other) is patterned by the lithographic method, and further the gate oxide film 203 and the poly-crystal silicon layer 204 are removed at only the predetermined ohmic contact portion between the gate electrode and the diffusion layer in accordance with the anisotropic etching technique (against the poly-crystal silicon) and the ammonium fluoride etching technique (against the gate oxide film), in order to form a contact hole 206.

Further, a tungsten siliside layer 207 with a film thickness of about 1000 Å is deposited all over the surface thereof by the sputtering technique.

Successively, as shown in FIG. 3E, BF₂ ions are implanted into the tungsten siliside layer 207 at the acceleration energy of 65 keV and the dose of 5×10¹⁵ cm⁻². Further, the impurity in the tungsten siliside 207 is diffused into the silicon semiconductor substrate by annealing at 800° C. for about 60 min to form a P⁺ diffusion layer 208.

Further, as shown in FIG. 3F, BF₂ ions are again implanted at the acceleration energy of 35 keV and the dose of 3×10¹⁵ cm⁻² to form a P⁺ diffusion layer 208a by using the gate electrode (the gate oxide film 203 and the poly-crystal silicon layer 204) as a mask.

In the above-mentioned second embodiment, in the same way as with the case of the first embodiment, since the ohmic contact between the gate wiring (the poly-crystal silicon layer 204) and the impurity diffusion layer 208a can be attained by intervening the metal (the tungsten siliside layer 207) of polyside structure, it is possible to enable an ohmic contact between the gate electrode 203, 204 and the impurity diffusion layer 208a whose conductivity types are different from each other, without use of any metallic wiring other than the polyside.

Further, in this second embodiment, after the tungsten siliside layer 207 has been deposited, the P⁺ diffusion layer 208 is formed in accordance with the ion implantation technique. Accordingly, there exists such an effect that the tungsten siliside layer 207 can reduce the damage caused by the ion implantation to the silicon substrate.

Further, the diffusion layer can be also formed by two different ion implantation steps, that is, the first ion implantation step (shown in FIG. 2C) into the substrate after the contact hole has been formed in the first embodiment and the second ion implantation step (shown in FIG. 3E) into the tungsten siliside layer in the second embodiment.

When the ion implantation is divided into two steps as above, it is possible to control the conditions (the acceleration energy and the dose) of each ion implantation, more freely and accurately.

Further, in the above-mentioned embodiments, tungsten siliside is used as the electrode wiring material. Without being limited thereto, however, various metals such as tungsten, molybdenum, titanium, cobalt, tantalum, etc. or other metallic siliside such as molybdenum siliside, titanium siliside, cobalt siliside, tantalum siliside, etc. can be also used.

Further, in the above-mentioned embodiments, although the gate electrode to which an N-type impurity is added is connected to the P-type diffusion layer, by way of example, it is of course possible to connect the gate electrode to which a P-type impurity is added to the N-type diffusion layer, in quite the same way as above, by changing the impurity.

As described above, in the manufacturing method of the semiconductor device according to the present invention, since the ohmic contact between the gate electrode and the impurity diffusion layer can be attained by use of the metal-containing material of polyside structure, it is possible to enable an ohmic contact between the gate electrode and the impurity diffusion layer different in conductivity type from each other, without use of any metallic wiring other than the polyside. Accordingly, even when a two-layer gate electrode including a poly-crystal silicon layer and an impurity diffusion layer (both of which are different from each other in conductivity type) are required to be connected to each other, as with the case of the CMOS circuit of the SRAM memory cell, no metallic wiring other than the two-layer wiring is required, thus promoting the microminiaturization of the semiconductor device markedly, so that the practical effect is extremely high. 

What is claimed is:
 1. A semiconductor device comprising:a silicon substrate of a first conductivity type; an impurity diffusion layer of a second conductivity type opposite to the first conductivity type, formed on a surface of said silicon substrate; at least first and second two-layer gate electrodes, each being formed of a polycrystalline silicon layer of the first conductivity type covered with a metal silicide layer, each electrode formed over an oxide film and said silicon substrate; and a contact hole formed on a part of said oxide film and said first and second gate electrodes, passing through said oxide film to a surface of said impurity diffusion layer to separate said first and second gate electrodes,wherein the metal silicide layer that is one of the two layers of the first two-layer gate electrode is formed so that a portion of the metal silicide layer contacts the impurity diffusion layer via said contact hole for attaining ohmic contact between said first gate electrode and said impurity diffusion layer of said second conductivity type through said contact hole.
 2. The semiconductor device of claim 1, wherein a simple melting point metal is included in the metal silicide layer.
 3. The semiconductor device of claim 2, wherein the high melting point metal is any one of tungsten, molybdenum, titanium, cobalt and tantalum.
 4. A semiconductor device comprising:a silicon substrate of a first conductivity type; an impurity diffusion layer of a second conductivity type formed in said silicon substrate; an insulating film formed over said silicon substrate; first and second silicon gate electrodes of a first conductivity type formed on said insulating film; a contact hole formed adjacent to and between said first and second silicon gate electrodes and through said insulating film to said impurity diffusion layer; and a wiring layer covering said first and second silicon gate electrodes and at least a portion of said impurity diffusion layer, wherein said wiring layer forms an ohmic contact between at least one of said first and second gate electrodes and said impurity diffusion layer of said second conductivity type through said contact hole; and wherein said wiring layer comprises a high melting point metal.
 5. The semiconductor device of claim 4 wherein said semiconductor device is a MOS transistor.
 6. The semiconductor device of claim 4 wherein said wiring layer comprises a silicide of a refractory metal.
 7. The semiconductor device of claim 5 wherein said insulating layer is an oxide of silicon.
 8. The semiconductor device of claim 7 wherein said wiring layer is in contact with said insulating film only along a portion of an edge of said contact hole. 